| Earthworm sensitivity The nervous system coordinates the movements of the animal and sends impulses received from sense organs to certain parts of the body. There is a very small nerve center in segment 3. From it run two nerves that form a connecting collar around the pharynx and join to become a long ventral nerve cord. There also are enlarged nerve centers, called ganglia, in each segment. Three pairs of nerves, in turn, branch from each ganglion. The earthworm has neither eyes nor ears, but is nevertheless sensitive to light and sound. Certain cells in the skin are sensitive to these stimuli, and the impulses are carried rapidly to the muscles of the earthworm. |